Platelet activating factor (PAF) is the most recently recognized and possibly the most potent cell-derived mediator of inflammation of bronchoconstriction. PAF is a small ether lipid and its structure from stimulated rabbit or hog leukocytes is known to be 1-0-alkyl-2-acetyl-sn-glycerol-3-phosphorylcholine or AGEPC or PAF-acether. An identical or similar molecule is released from appropriately stimulated human blood granulocytes and macrophages, alveolar macrophages, endothelial cells, platelets themselves and from other cells in other species. PAF-acether or AGEPC activated platelets and causes them to aggregate and secrete constituents such as serotonin, ADP and prostaglandins. PAF also aggregates human granulocytes either directly or indirectly via the leukotriene B4 pathway, induces some systemic hypotension, induces airway and ileal contractions, induces pulmonary edema, and evolving data indicate it plays an important role in inflammation. Human, rabbit and rat sera contain an acid labile factor (ALF) that rapidly inactivates PAF in vivo and in vitro. ALF has proved to be a highly specific PAF-acylhydrolase that deacetylates AGEPC to its inactive lyso GEPC form. The recognition of the presence of PAF-acylhydrolase, together with learning how to inactivate the enzyme before it degrades PAF newly released into plasma in vivo, has led to the extraction of a PAF-like lipid (PAF-LL) from humans during cold-induced urticaria. In addition, inordinate amounts of PAF-LL are present in the sputums and nasal washes of patients with asthma, bronchitis and sinusitis. Preliminary experiments indicate it is released in human asthma induced by antigen bronchial provocation tests. This application proposes to extend these observations that PAF-LL may play an important role in human allergic and inflammatory diseases. Also, methodology has been developed to prepare highly purified human PAF-acylhydrolase. It is now feasible to raise and rapidly screen for monoclonal antibodies directed towards PAF-acylhydrolase preferably towards the enzymatic site. The antibodies will be used to develop a much needed accurate and rapid immunoassay to measure changes in PAF-acylhydrolase levels in human disease states. Thus, the overall objectives of this project are to better understand the interaction, in human health and disease, between the production of PAF and the control of PAF activity by PAF-acylhydrolase.